text: The third, and best performing, class of ferric tapes is made of fine ferric particles encapsulated in a thin  layer of cobalt-iron mix, similar in composition to cobalt ferrite.  The first cobalt-doped cassettes, introduced by 3M in 1971, had exceptionally high sensitivity and MOL for the period, and were an even match for contemporary chromium dioxide tapes — hence the trade name superferrics. Of many competing cobalt-doping technologies, the most widespread was low-temperature encapsulation of ferric oxide in aqueous solution of cobalt salts with subsequent drying at 100150°C. Encapsulated microferric particles retain needle-like shape and can be tightly packed into uniform anisotropic layers. The process was first commercialized in Japan in the early 1970s.
  The remanence of ferricobalt cassettes is around , resulting in around  gain in MOL and 23dB gain in sensitivity compared to basic Type I tapes; their hiss level is on par with contemporary microferric formulations. The dynamic range of the best ferricobalt cassettes (true superferrics) equals 6063dB, and the MOL at lower frequencies exceeds the MOL of Type IV tapes. Overall, superferrics are a good match to Type IV, especially in recording acoustical music with a wide dynamic range. This was reflected in the price of top-of-the-line superferric tapes like Maxell XLI-S or TDK AR-X, which by 1992 matched the price of entry-level metal tapes.